Types of registers

There are three usual type of registers (shared variables) that are
used in asynchronous systems:
safe, regular and atomic (from the weakiest type to strongest type).
Is anyone know about possibilty to get interprocess communication using
less-than-safe registers? At least satisfy mutual exclusion (no two
process in critical section at the same time).
Less-than-safe means that parallel operations(reads or writes) have
arbitrary result.

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